The tetrad relationship uses four colors that are chosen from every third color on the color wheel. Like the triad relationship, the name tetrad comes from the shape made between the colors. Orange/yellow-green/blue/red-purple is just one example.
A Triad is a combination of 3 colors that are equidistant from each other on the color circle. It produces a high contrast effect while preserving ’harmony.’ Such a composition looks vibrant even when you use pale and unsaturated colours.
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